Curable polyester resin systems have been widely used in varied applications, such as in polyester body filler systems and glass reinforced polyester body filler systems used in the automotive body repair field where body filler systems are used to fill dents, and also, when provided with glass reinforcement, are used for filling holes in body panels and the like. Such systems are usually designed to cure to sufficient strength and to sandable condition within twenty minutes. However, while the polyester resin filler systems, both unreinforced and reinforced, adhere securely to properly prepared steel body parts, they have poor adhesion to many substrates such as hot dipped galvanized steel, copper, bronze, tin, solder, brass, stainless steel, aluminum, glass (silicon oxide) and the like. The poor adhesion characteristics of the polyester resin dent and polyester resin hole filler systems present substantial problems in their use and thus, for an extended period of time, such problems have been recognized as continuing problems which effectively limit many uses of the polyester filler systems.
In the case of hot dipped galvanized substrates, the poor adhesion problem is aggravated by the fact that the galvanize (zinc) retards curing of the resin system, delaying sanding and further operations on the filler, and, in some cases, may prevent a full cure. The failure of the filler system to fully cure results in the poor adhesion to the substrate being weakened even further and the filler having reduced cohesive strength as well.